hey got a ?...when i changed the plugs to the NGKs the old ac delco plugs were red? what is that from..i took a knife and could scrape it off the inside...it wasnt a blood red more like a glowing red..like they were red hot..but they werent hot any takers

 

Do you use gas additives? That's a sign of that.

 

http://www.dansmc.com/Spark_Plugs/Sp...s_catalog.html